The present invention relates to an engine generator comprising an engine and a generator driven by the engine. In particular, this invention relates to an engine generator capable of cooling the engine by means of a cooling fan driven by the engine.
Conventionally, as an electric power source for use in an outdoor condition as a road construction, a road repairing operation, or an out-door shop and leisure service, there has been in use an engine generator comprising an engine and a generator driven by the engine, both of which are enclosed in a housing so as to form an arrangement capable of producing an electric power. In fact, such an engine generator is so constructed that a rotor equipped with several pieces of magnet is fixed on a crank shaft, in a manner such that the rotor can rotate in the vicinity of a stator equipped with a plurality of coils, thereby generating an electric power. In order to cool the engine and the generator as well as a muffler, a cooling fan driven by the engine is provided within the housing. In this manner, with the rotation of the crank shaft, the cooling fan can also be rotated, thus forming an arrangement capable of introducing an outside cool air into the housing so as to cool the engine and the generator as well as the muffler.
Japanese Unexamined Patent Laid-open Application Publication No. 11-36880 has disclosed an improved cooling structure suitable for use in an air-cooling type engine generator equipped with a cooling fan. This patent publication teaches that an outer rotor type generator may be used, and a housing encloses the generator, an engine and a muffler, which are arranged successively and covered by a duct and a fan cover. Further, the prior art publication discloses that a cooling fan is attached to the outside of the outer rotor of the generator, in a manner such that the cooling fan can rotate together with the crank shaft of the rotor, thereby introducing an external cooling air into the housing. In fact, the cooling air is rendered to at first cool the generator having a relatively low temperature, then the engine and the muffler (both of which have a relatively high temperature). Finally, the used cooling air is discharged to the outside of the housing.
However, with the above described engine generator disclosed in the above mentioned patent publication, the muffler is cooled only after the engine has been cooled, the cooling air for cooling the muffler is air already used in cooling the engine and thus is a warm air. As a result, the efficiency of cooling the muffler is lower than a condition in which the muffler is directly cooled by an outside cold air.
It is an object of the present invention to obtain an improved cooling efficiency for an engine generator by dividing a cooling air passage into two routes, with one cooling the cylinder head of the engine, while the other the oil pan and the muffler, so as to solve the above-mentioned problem peculiar to the above-discussed prior art.
An engine generator of the present invention comprises a base, an engine disposed on the base; a generator driven by the engine; a muffler positioned on the exhaust side of the engine; a cooling fan driven by the engine; a housing enclosing the engine, the generator, the muffler and the cooling fan; a first cooling air passage formed on the cylinder head side of the engine for cooling the upper portion of the engine by a cooling air supplied from the cooling fan; and a second cooling air passage extending from the lower side of the cooling fan and passing under the lower side of the engine and arriving at the muffler for cooling the lower portion of the engine and the muffler by said cooling air supplied from the cooling fan.
According to the present invention, the cooling air has been divided into two routes, with one being used only for cooling the cylinder head and the other for cooling the lower portion of the engine and the muffler. In this way, it is possible to cool both the upper and lower portions of the engine, while at the same time ensuring that a cooling air for cooling the muffler has a lower temperature than that of an air which has just been used for cooling the cylinder head of the engine.
Further, since an oil pan of the engine is disposed to face the second cooling air passage, it is possible to use a cooling air flowing through the second cooling air passage to effectively cool the oil pan located on the underside of the engine.
In addition, it is possible that the second cooling air passage may be interposed between the oil pan of the engine and a vibration isolation support base plate attached under the lower side of the engine and extending in the extending direction of the crank shaft of the engine, thereby rendering it possible to form the second cooling air passage by effectively making use of the engine support structure. On the other hand, it is also possible to inhibit the propagation of an engine vibration, based on that vibration isolation members interposed at the end portions of the vibration isolation support base plate.
The above objects and features of the present invention will become better understood from the following description with reference to the accompanying drawings.